General Review of Present Concepts of Cyclic Deposition

For a little more than a decade nearly all students of Pennsylvanian and Permian rocks have been cognizant of cyclic sedimentation that occurred on scales intermediate between that of very short time repetitions, such as are represented by varves, and those represented by the great transgressive and regressive phases that characterize time-rock units, the series or larger divisions. These cyclic deposits are commonly called cyclothems, but after the introduction of the term megacyclothem (Moore, 1936, pp. 21-38) it has been plain that depositional cycles of two or more magnitudes can be recognized in some rock sections. Megacyclothems as recognized in Mid-Continent Pennsylvanian strata consist of several smaller cyclic units. Attention has been called to the probability that megacyclothems may be recognized in areas where cyclothems already are known and that some "cyclothems" may be identified as megacyclothems (Jewett, 1941, p. 343). Partly because of looseness of definitions and partly because of progress in detailed knowledge of the rocks, clarification of terms seems to be essential. It is very probable, however, that systematic classification of these intermediate cyclic deposits must await still more detailed stratigraphic and sedimentary studies.

Wanless and Weller (1932, p. 1003) defined cyclothem as a series of beds deposited during a single sedimentary cycle. Weller (1930, p. 99) previously defined cycle as a recurrence, repetition, or return to the starting point. This definition of cyclothem could, perhaps, be applied to varves, annual deposits recording the march of the seasons, or to large transgressive and regressive units having the magnitude of geologic series or even systems. Obviously, however, the intention was not to include such extremes of sedimentary cyclic units. Elias (1937, p. 408) in discussing cyclic deposits in the Big Blue (Wolfcampian) series in Kansas, stated that the cyclic units are intermediate between the minute seasonal rhythms of varved clays and the great cycles of geologic periods. Such statements are not especially helpful because it is evident that rock units called series are in many cases cyclic units and it is commonly agreed that these units are larger--that is to say, are thicker--and represent a greater amount of time than the units commonly called cyclothems. Weller regards cyclothems as roughly having the magnitude of formations, and Moore has identified megacyclothems that roughly correspond to formations in Kansas. Of course the classification of rock units into formations has come about because of the more or less obvious differences in lithology in successive beds; in places like Illinois and Kansas, where Pennsylvanian rocks have been studied in great detail, the formations are the easily differentiated, mappable units, and are of about the same time span.

As an example of the use of terms in an important recent stratigraphic paper, it is noted that McKee (1938, p. 130) stated that both the Toroweap and Kaibab (Permian) formations in northern Arizona and southern Utah are thought to be true cyclothems, and that the members they include are equivalent to "phases" as the term is used by Moore. Moore (1936, pp. 28, 30) used the term phase to indicate one of the units making a cyclothem. McKee (1936, p. 132) recognized numerous "minor cycles" in the Kaibab formation.

The classificatory system including (1) varve, (2) phase, (3) cyclothem, and (4) megacyclothem is well established. It is, of course, understood that cyclothems are not commonly divisible into varves, but it is recognized that varves are cyclic deposits and it is probable that varves will be recognized in Paleozoic rocks. According to usage, megacyclothems consist of two or more cyclothems of different character that occur in regular sequence; phases are units within cyclothems. Hence, the term cyclothem seems properly used to designate in any area the smallest recognizable cyclic units except varves. It is held that if the term cyclothem is used it should be in this sense and that the term megacyclothem should be used to indicate a unit, cyclic in itself, but composed of two or more cyclothems.

Moore (1936, p. 23) has proposed that cyclic deposits of the northern Mid-Continent region be designated by the names of the limestones that each contains. This practice can be followed when working in most parts of the Pennsylvanian section, but it is necessary to use the names of some other kinds of rock in the Cherokee shale. Abernathy (1937), who identified and named 15 cyclothems in the Cherokee shale, used principally the names of coal beds to designate cyclothems.

Fifteen cyclothems are known in Cherokee rocks in Kansas. It is believed that there are four well-developed megacyclothems of four or more cyclothems each in the Marmaton group in Kansas. Moore (1936, p. 23, fig. 10) has identified four megacyclothems in the Shawnee group. Cyclic deposits in rocks between the Marmaton group and the Shawnee group seemingly are not so distinctly developed in the outcrop belt, and exact numbers can not be given so definitely. It is to be noted, however, that cyclic deposits are clearly discernible and are very obvious in several parts of the section. The Wabaunsee group, overlying the Shawnee rocks, is divisible into several cyclothems, but there the grouping of cyclothems into megacyclothems is not evident.

Wanless and Shepard (1936) reviewed the literature on Pennsylvanian and Permian cyclic deposits. They found that cyclic sediments of Pennsylvanian age had been described from Illinois, Kansas, Iowa, West Virginia, Michigan, Texas, Colorado, British Isles, and the Silesian basin. They pointed out that described sections of Pennsylvanian rocks in many parts of the world indicate the presence of cyclic deposits.

There are several recent stratigraphic papers, in which cyclic deposition is not discussed, that nevertheless clearly indicate cyclic sedimentation in their descriptions and graphic sections. Here may be noted the Pennsylvanian sections described in (1) the Appalachian valley in Virginia (Butts, 1940); (2) the Muskogee-Porum district of Oklahoma (Newell, 1937); (3) Washington county, Oklahoma (Oakes, 1940); and (4) New Mexico (Thompson, 1942).

It was noted by Wanless and Shepard (1936) that the period of earth history marked by cyclic sediments in the central part of the United States of America seems to extend from about the end of Meramecian, through Chesterian (Late Mississippian) and throughout all of Pennsylvanian and early Permian time. The presence of cyclic deposits in rocks of Chesterian age was noted by Wanless and Shepard (1936, p. 1180) and Permian cyclic deposits have been noted by McKee (1938), by Elias (1937), and by me (Jewett, 1933). The compilation of the number of cyclothems in Pennsylvanian rocks by Wanless and Shepard seems too small, however, in the light of present knowledge. They assigned 38 to the Pennsylvanian. We now know of more than 30 in the Desmoinesian rocks alone (Abernathy, 1937a, p. 19; Jewett, 1941, p. 288).

It is commonly believed that these types of cyclic deposits have resulted from fluctuations in relative height of sea level-and that cyclothems are widespread. The theories as to the causes of sea-level fluctuations will not be discussed fully here, but attention is called to the hypothesis of Wanless and Shepard (1936) postulating that waxing and waning of glaciers caused the sea-level variations. It has been pointed out that four cyclothems in Illinois are recorded in a certain section of rock and that the same number of megacyclothems are known in Kansas rocks which are believed to be of approximately equivalent time span. It must follow, then, that these Kansas megacyclothems are equivalent (if they resulted from the same casual factors) to the Illinois cyclothems. In spite of this seeming misuse of terms in one place or the other, it is held that the usage is good. In both places the term cyclothem is used for the smallest cyclic unit that has been recognized.

It is evident that more minute changes in the elevation of sea level could not have been equally well recorded by changes in rock material in all places where sediments were accumulating. Marmaton rocks in their outcrop area in southeastern Kansas are more dominantly calcareous and a greater part is of marine origin than rocks of the same age in Illinois. The relatively short time and seemingly shallower sea invasions of eastern Kansas did not reach as far eastward as Illinois. Rocks of Missourian age are divisible into cyclothems and megacyclothems in eastern Kansas but equivalent rocks form a nearly solid limestone section farther west in the state. Minor changes in sea-level elevation were not so effective there.

Knowledge of cyclic sedimentation is not new. More than 120 years ago Conybeare and W. Phillips remarked on the rhythmic manner in which clay is followed by sand and sand by limestone in the oölitic sequence of Britain. This principle of cyclic sedimentation, which was established at about the same time that William Smith was laying the foundations of stratigraphy, has been used by several subsequent European students of Mesozoic rocks. A rather casual survey of European stratigraphic literature shows that the principle of cyclic deposits was a commonly accepted tool in stratigraphy during the first two decades of the present century and that much earlier cyclic deposits, as least in the Jurassic, were known to be widespread. The first modern stratigraphers to recognize the really important bearing of cyclic deposits on problems of stratigraphy are Andrée (1908), Klüpfel (1916), and Frebold (1924). Arkell (1933) was fully cognizant of their bearing on studies of the Jurassic of Great Britain.

Although cyclic sediments in American Paleozoic rocks were recognized earlier, it was only a few years ago that their significance and usefulness in Pennsylvanian stratigraphy were emphasized. The recent advancement of studies of cyclothems and stratigraphy based on cyclic units is due chiefly to the researches of J. M. Weller, H. R. Wanless, and their associates in Illinois, and of R. C. Moore and his co-workers in Kansas. It is now evident that numerous stratigraphic problems can best be solved through the study of cyclic units. An example that may be cited here is the question of the true relationships of beds in the Cherokee shale in eastern Oklahoma and eastern Kansas. It does not seem to be out of place to remark that the principle of cyclic deposition ranks with paleontology in usefulness in studies of many parts of the Pennsylvanian rock section.

Modern students of British Carboniferous rocks seem to be fully aware of the significance of cyclic sedimentation. Richey (1937, pp. 96-99) described rhythmic cycles in the Carboniferous limestone and oil shales of Scotland. Tonks and Jones (1931, pp. 10-13) described sedimentation cycles in the Carboniferous of Manchester; Robertson (1932, pp. 87-89) described cyclic sediments in the South Wales coal-field; and Trotter and Hollingsworth (1932, pp. 17-19) discussed the same features in the Brampton district.

Three principal types of hypotheses to explain cyclic deposits have been advanced. They are (1) that cyclic sedimentation recorded intermittent subsidence, contemporaneous with and followed by sedimentation, and then renewed subsidence; (2) that it recorded diastrophic. movements alternating between subsidence and uplift; and (3) that it recorded sea-level fluctuations caused by storing of ocean water on land in the form of continental glaciers or as interior seas or lakes.

An hypothesis of the first type was advanced as early as 1871 by J. Phillips. Much later Stout (1931) and Cady (1934) sought to explain Pennsylvanian cyclic deposits in the same way. Weller (1930) formulated an hypothesis of alternating subsidence and uplift, and Wanless and Shepard (1936) are the authors of the theory of fluctuating sea level brought about by storing of ocean waters on the land. They placed special emphasis on the probability that Late Paleozoic glaciation caused cyclothems. Richey (1937, p. 96), in writing of cyclic sedimentation in the Lower Carboniferous of Scotland, stated that the strata were lain down over a gradually sinking area, that the strata repeatedly raised the surface within reach of the growth of vegetation, and that the rhythmic sequence may all be explained by supposing that subsidence took place spasmodically.

Evidence of Cyclic Sedimentation in Marmaton Rocks

The presence of four large cyclic units in the Marmaton group is obvious. There are four limestone formations, each underlain and overlain by elastic formations which consist principally of clay and sandy shale but contain a relatively large amount of sandstone, a part of which fills definite channels whose walls are of clay shale and limestone. A more or less persistent deposit of "underclay" and coal lies above each limestone formation. Thus it seems that the Fort Scott, limestone, a part of the underlying Cherokee shale, and the lower part of the overlying Labette shale are a cyclic unit. The Pawnee limestone and a part of the overlying Bandera shale constitute another megacyclothem next above the upper part of the Labette shale. Still higher the Altamont limestone is underlain and overlain by elastic deposits, and especially the Bandera Quarry sandstone below the Altamont formation records the beginning of sedimentation after channeling took place. The fourth large cyclic deposit, near the top of the Marmaton group, consists of the upper part of the Nowata shale, the Lenapah limestone, and the overlying Memorial shale or at least the lower part of it. Thus it is convenient to speak of four megacyclothems: (1) the Fort Scott, (2) the Pawnee, (3) the Altamont, and (4) the Lenapah.

These four well-defined and relatively large cyclic units in the Marmaton rocks are called megacyclothems chiefly because the thinner shale units included within the limestone formations may be only partly marine and they certainly record an approach of the shore line. Each of the thinner shales contains in the middle part either black shale or black shale, coal, and underclay. Thus each of the thinner shale units contains a phase that marks the end or beginning of a cycle.

Typical cyclothems in the Wabaunsee group (Moore, 1936, p. 23, fig. 2) are similar to those in the Marmaton group, and it is reasonable to suppose that the Wabaunsee rocks when they were exposed farther east, before erosional beveling had placed their outcrops in the present geographic position, may have contained more phases of nonmarine shale, for example in "phases .4 and .6." At their present outcrops these phases of Wabaunsee cycles bear a molluscoid fauna and are regarded as phases of cyclothems, as are their homologies in outcropping Marmaton rocks.

The four limestone formations of the Marmaton group generally contain four or more distinct cyclothems that represent marine invasions. The shale formations include several cyclothems which seem to be dominantly nonmarine, but minor and somewhat local marine invasions are recorded in some of the cyclothems included in the shale formations. Each of the larger cyclic units (roughly the four limestone formations) presents evidence of three, four, or more distinct marine invasions of a large area. Thus the Marmaton rocks in their Kansas outcrop belt contain at least 15 well-developed cyclothems and several poorly developed ones. The latter are included in the shale formations.

In spite of the voluminous literature dealing with sedimentation and interpretation of fossil sediments, little can be said with exactness concerning the conditions under which sedimentary rocks were formed. In some cases, perhaps in many, marine and nonmarine sediments cannot certainly be distinguished. Nevertheless in studies of this kind it is well to call attention to the significance of various rock types. There are some deductions that seem to be sound. Because of their repeated occurrence as cyclic phases, the probable origin of several rock types is briefly discussed here.

In discussing the sequence of major events during a typical megacycle of Pennsylvanian rocks, Wanless and Shepard (1936, p. 1202) denied that the sandstone that fills channels is material derived locally because the sandstones are composed largely of micaceous sands and the walls of the channels are of clay shale and limestone. However, in eastern Kansas and in western Missouri only locally have the channels been cut into limestone and in eastern Missouri, where the channels more commonly are cut into limestone beds, the basal parts of the channels are frequently filled with locally derived limestone fragments. It is likewise true that in these rocks the occurrence of sandstone as channel fillings is the exception rather than the rule and that great quantities of micaceous sandstone grade laterally into clayey shale. Locally channels were cut into sandy shale and sandstone. Because of the absence of sufficiently large areas of near-by quartzose rock that were exposed in Late Desmoinesian time and because of the fineness and the degree of sorting of the quartz grains, it is evident that the primary source of the micaceous quartz sandstone was not near by. Igneous rock mineral species other than mica and quartz are practically absent from these Marmaton sandstones. At least some of the mica may be of secondary origin, although there may be little basis for that assumption. The primary source of the quartz sand, like the clay in the shale beds, must have been a distant terrain.

Sandstone is abundant in the Pennsylvanian section farther south and east, and sandy sediments including sandstone form a part of the conformable sequence of these rocks throughout the Mid-Continent region. It is reasonable to believe that the sandstone that now fills the channels is reworked material from near-by sources.

The channels themselves require explanation. The large and deep channel that contains the Warrensburg channel sandstone in Missouri seems to extend northward off the Ozark dome. At the present time little can be definitely said about the direction or pattern of other channels, although it is probable that several radiate from the Ozark region. This is suggested by the facts that several channels are deeper in places near the Ozarks and that the basal part of the fillings there are limestone conglomerates. It is suggested here that the channels were probably cut by water draining from or across slightly uplifted or tilted areas. It is postulated that large areas were essentially flat and were near sea level immediately before channeling. Sand and silt ranked high in quantitive importance in sediments that were accumulating. Either because of differential subsidence or subsidence and uplift, comparatively small areas were placed in such a position that surface water drained across them with sufficient velocity to cut channels a few feet deep in the soft sediments. Abrupt lateral changes in thickness of shales suggest local intraformational movements. While cutting the channels the flowing water carried sand, silt, and clay beyond the channels into more depressed areas where it was deposited in conformable beds. Later the channels were filled with sand and silt while clay was probably being carried farther from the source. After the channels were filled, sandy deposits were spread with apparent conformity on the slightly older clays and sands in which the channels had been cut.

Bass (1936) has presented convincing evidence that Cherokee shoestring sand bodies in Greenwood and Butler counties, Kansas, were formed as offshore bars in a shallow sea. It is entirely probable that some of the Marmaton sandstone lenses had a similar origin. However observations show that at least some of them fill definite channels cut in beds of shale and limestone.

Cross-bedding in Marmaton sandstones in eastern Kansas is comparatively rare. Both the sandstones that occur in more or less lens-like masses, which are seemingly conformable with clay shale, and those that fill definite channels are thin bedded. Ripple marks are plentiful. Fossils are almost nonexistent except for remains of land plants which occur locally. One exception is the local occurrence of myriads of fossil annelids in the Bandera Quarry sandstone at a place where it seems to fill a channel. The presence of land-plant remains indicates that now and then deposition built up near-by terrains to within the reach of the growth of vegetation, but the plant remains, consisting mostly of stem fragments, are not now in the places in which they grew. Fossil fern leaves, found abundantly in some other Pennsylvanian sandstones, are rare in Marmaton rocks.

In summary it is pointed out that Marmaton sandstones occur in large lenses but that the lower part of the masses locally occupy channels and that the lower parts of the channels locally are filled with limestone breccia or conglomerate. The sand is fine, indicating that it was carried a great distance from its primary source or that it has been shifted by waves for a long time. In the channels, and locally elsewhere, the sand is remarkably free from clay, which indicates that here and there are deposits of reworked quartz grains and mica flakes. In general, the primary structure of the sand deposits indicates deposition under quiet conditions.

Thick beds of gray shale in the Marmaton group generally are more or less sandy, but locally they are almost entirely without sand grains. These shales are seemingly nonfossiliferous. They grade vertically and laterally into sandy shales and, like the sandy shales, they are evenly and well bedded. However, the gray shale that occurs in thick beds as a part of the shale formations occurs in "blocky" beds which contrast with thinner bedded, fissile, or platy shale. Stringers and small lenses of limonite are common in these gray shales, and at the outcrops the rocks are locally yellow or yellowish-gray in color.

It is believed that the thicker gray shale beds were deposited at a position near sea level--probably generally slightly below sea level. They record events that took place near the beginning and end of the large cycles of deposition and are in part contemporaneous with sandy shales and sandstones. Locally this type of gray shale embraces other kinds of rock, such as thin-bedded fossiliferous gray shale, black platy or fissile shale, coal, and limestone, which seems to record local and short-time incursions of the sea or deepening of sea water between periods of greater elevation. These sequences within thick shale formations are local and incomplete cyclothems. In the Kansas outcrop belt of Marmaton rocks they are best developed in the Labette shale.

Thinner deposits, consisting of gray and commonly greenish-gray shale, thin-bedded or even fissile, and commonly bearing marine fossils, brachiopods, crinoid fragments, and locally corals, are distinguished from the more blocky gray shale that is predominant in the shale formations. These thinner shales commonly lie next below and above limestones. Shales of this kind, where separating limestones within the limestone formations, at least locally are themselves divided in their approximate middle parts by black shale or by black shale and coal. These calcareous fossiliferous thin-bedded shales seem to record transgressions and regressions of sea water, whose maximum stages of invasion were marked by limestone deposition. Although any of the cyclothem phases may be absent locally, they occur normally above black shale or black shale and coal and below limestone.

Much of the black shale in Kansas Marmaton rocks is platy rather than fissile. The bedding, which is always well pronounced at the outcrop, ranges from paper-thin to one-fourth inch or more. In underground workings or as seen in cores taken from wells, black shale of this kind displays little or no bedding and has the appearance of black massive rock. Bedding in these shales probably is partly slaty cleavage which becomes apparent after weathering. The layman's term "slate" for this rock is probably not altogether inappropriate. Where coal is associated with black shale, the coal commonly underlies the carbonaceous shale. A few exceptions to this have been noted, but thin coal beds, coaly concretions, and shale that is nearly coal occurring in black shale evidently are detrital. Small phosphatic concretions which are roughly spherical and generally smooth commonly occur in black shale deposits. Linguloid and orbiculoid brachiopod shells, generally believed to have lived in brackish muddy waters, are more or less commonly present. It is believed that this type of black shale was formed through deposition of muds which were black partly because of underlying peat beds in their source area and partly because of shallowness of the water which produced stagnant conditions. In the cyclothem record, black shale indicates the former presence of shallow near-shore water, free from sand. The source areas were low and covered by vegetation.

Coals in Marmaton rocks commonly underlie black shales. In some places they are underlain by "underclays." One of the most persistent coal beds is the Mulberry coal which occupies a position near the base of the Bandera shale. The Mulberry coal is one of the thicker beds and whenever present it seems to be underlain by "underclay." This coal deposit is believed to be typical of Marmaton coal beds that were formed through accumulation of plant material at the place in which it grew. Evidence of such deposition includes the facts that the coal lies above an "underclay," is relatively free from ash, and is of widespread occurrence.

The presence of the Summit coal, which occupies a position in the Little Osage shale, indicates that the sea withdrew completely from a part of eastern Kansas during the closing stages of the Blackjack Creek cycle (lower cyclothem of the Fort Scott megacyclothem). This coal is underlain by gray shale which has some of the characteristics of ail underclay. The coal is laterally persistent for many miles, and it is relatively free from ash. The Summit coal is believed not to have been of detrital origin. There are several similar coals in the Marmaton rocks, particularly a short distance above each limestone formation.

It is evident that limestone records the former presence of marine water relatively free from land-derived detrital material. No limestone beds in the Marmaton group in the northern Mid-Continent region are recognized as fresh-water limestones. The several different types of limestone, however, present special problems of origin. In Marmaton time in eastern Kansas, calcareous sediments deposited in places relatively near the shore commonly developed thin slabby-bedded structures or developed into a massive layer of impure limestone with little or no bedding. Calcareous nodules not sufficiently plentiful to form continuous beds but enclosed in clay were formed in places where the accumulation of clay greatly exceeded the precipitation of lime.

Thin-bedded wavy-bedded limestone, common in the Pennsylvanian section in this part of the world, was developed in places which at the time were covered by clear sea water and probably were relatively far from shore. In late Desmoinesian time Chaetetes colonies flourished under similar conditions, seemingly crowding out most of the other bottom-dwelling invertebrates. Pseudobrecciated limestone commonly occurs in thin beds and is relatively free from land-derived detritus. The brecciated appearance is probably of secondary origin; its significance is not certainly known. Algal remains are plentiful in both impure and purer limestone in the Marmaton group. Fusulines occur in the thicker limestones and do not seem to be restricted within the thicker beds. Brachiopods range through black shales, gray shales, and limestones of varying degrees of purity, but mollusks are confined to what seems to be shallow water limestones and marine shales which commonly are nearly black.

The Fort Scott Megacyclothem

The Fort Scott limestone, including the underlying coal and elastic deposits and the overlying coal and elastic deposits, records a relatively large cycle of deposition, a megacyclothem. Smaller cycles within the larger one are detectable.

Several Kansas outcrops, for example the ones represented by sections 108 and 111 of plate 1, give the impression that the limestone bed in the upper part of the Cherokee shale lies in the lowermost cyclothem of the larger Fort Scott cycle. Observations in Craig and Rogers counties, Oklahoma, however, indicate that this limestone in Kansas, the Breezy Hill, may lie in the third or fourth cyclothem below the Fort Scott limestone. It is believed that cyclic deposits between that of the Breezy Hill limestone and the Blackjack Creek limestone are confined to a narrow zone in northeastern Oklahoma and that in southeastern Kansas and at some places in eastern Oklahoma there is a hiatus in the upper part of the Cherokee shale. This is not conclusive, however; the problem is one of several similar ones that may be solved through detailed study of Cherokee cyclothems.

The Mulky coal, the "underclay" below it, and the overlying black shale, which locally contains giant black concretions, are believed to belong in a cyclothem with the overlying Blackjack Creek limestone rather than with the Breezy Hill limestone. The "underclay" and coal record nonmarine deposition. Advancement of the sea over peat beds seems to be recorded by the black shale; calcareous shale, next below the Blackjack Creek limestone, recorded slightly deeper and clearer waters. The Blackjack Creek limestone records the maximum sea invasion of the lowermost Fort Scott cycle. The basal part, massive impure limestone called the "Cement rock," is characteristic of the basal part of several thicker Marmaton limestones. It represents the beginning phase of limestone deposition in cyclothems containing relatively thick limestones. It is the kind of limestone that locally was succeeded by purer thin-bedded and commonly coralline limestone deposition. Chaetetes biostromes were deposited locally on the "Cement rock" substratum, while the clearing of the water promoted the deposition of purer calcium carbonate, commonly in thin and wavy beds. Locally a few inches of slabby impure limestone occurs as the uppermost part of the Blackjack Creek limestone. Faunal phases in the Blackjack Creek limestone are not very well defined, but the following succession with some vertical overlap can be detected: (1) mollusks and crinoids, (2) Chaetetes and brachiopods, and (3) brachiopods and fusulines.

Local calcareous shale breaks in the "Cement rock" part of the Blackjack Creek limestone are found in places that are believed to have been relatively near the shore line at the time of deposition. Higher in the section an homologous limestone, the basal part of the Tina limestone, grades laterally into sandstone and shale. Calcareous fossiliferous gray shale overlain by the Summit coal is the closing phase of the Blackjack Creek cyclothem.

Shale, commonly black and slaty but paradoxically calcareous and containing marine fossils locally in the lower part, followed by the Houx limestone records the second sea invasion of the Fort Scott megacyclothem. In parts of eastern Oklahoma and southeastern Kansas the Houx limestone seems to be included in the Higginsville limestone as its lower part. In that area, which is believed to be a slightly deeper part of the depositional basin, the Houx and Higginsville cyclothems are not readily divisible.

The Higginsville cyclothem contains black shale, gray fossiliferous shale, and the overlying Higginsville limestone, which in turn is overlain by extensive black shale deposits and a relatively persistent coal bed. The Higginsville limestone displays faunal zones, more or less distinct and somewhat similar to those of the Blackjack Creek limestone. Chaetetes, however, was an important rock builder during the closing stages of this limestone phase, and algal remains are also plentiful in the upper part of the phase. It seems reasonable to believe that Chaetetes and algal deposits accumulated in shallow but clear waters. Molluscoid faunas, found in the earlier and later marine phases of several Pennsylvanian cyclothems, are associated with less pure limestone and with calcareous shale. These faunas indicate muddy waters.

The Pawnee Megacyclothem

Cyclothems in the Labette shale, the clastic formation that separates the Fort Scott and Pawnee limestones, are locally and poorly developed in Kansas. The scarcity of good exposures has prevented detailed study of these beds. Seemingly there are several poorly developed cyclothems above the Higginsville limestone in the Fort Scott megacycle. It is believed that a rather persistent unnamed coal bed in the lower-middle part of the Labette shale was deposited during the closing stages of the Fort Scott megacycle, and it is probable that a large part of the sandstone that collectively is called Englevale sandstone belongs in the upper part of the Fort Scott megacyclothem. Detailed study of cyclic deposits in such thick clastic deposits as the Labette shale will undoubtedly shed much light on Pennsylvanian paleogeography.

The Pawnee, megacyclothem in Kansas contains four well-developed cyclothems. They are, in ascending order, (1) the Anna (lower ? Oologah) cyclothem, (2) the Myrick Station cyclothem, (3) the Mine Creek cyclothem, and (4) the Laberdie cyclothem. All contain at least black shale, gray shale, and limestone phases. Actually there are more cyclothems, but only these four are sufficiently developed in Kansas to warrant names. There are several partly developed cyclothems in the upper part of the,Labette shale; locally these are divisible into coal, black shale, and limestone phases (pl. 2, sec. 181).

A rather persistent coal bed a few inches below the thin limestone that in Kansas is classified as the basal part of the Anna shale is believed to belong with this limestone in the Anna cyclothem. This relationship is not conclusively established because it is possible that lower Pawnee cyclothems, represented at least in part in eastern Missouri and northeastern Oklahoma (pl. 2, secs. 181 and 193), are absent in eastern Kansas. It is clear, however, that the Anna cyclothem is well developed in northern Oklahoma and that there is one and perhaps two cyclothems between it and the overlying Myrick Station cyclic unit. Black shale and the Lexington coal bed in the Anna shale mark the beginning of the Myrick Station cyclothem. Coal in the Anna shale in Kansas is probably detrital; hence, it is not correlated exactly with the Lexington coal of Missouri. The Lexington coal is believed to occur in Oklahoma (pl. 2, sec 203) where it is underlain by shale having some of the characteristics of an underclay.

The Myrick Station cyclothem starts with black shale or coal and black shale, which is overlain by a bed of gray marine shale. The black shale phase is also at least in part marine. Locally it contains sparse orbiculoid and linguloid brachiopods. A prolonged and widespread invasion of clearer sea water is recorded by the Myrick Station limestone. Brown massive impure limestone, similar to the Fort Scott "Cement rock," was formed over a great area in the beginning. It is believed that this is the part of the Myrick Station limestone that extends into Iowa and Illinois. This basal limestone was succeeded by purer thinner bedded limestone deposits. Chaetetes colonies became established early during Myrick Station deposition, but were more plentiful during the later stages. Abrupt clearing of the water seemingly permitted Chaetetes to start colonies on mud bottoms. This condition is more or less uncommon. Noncoralline limestone commonly underlies Chaetetes biostromes.

In general the Myrick Station limestone is divisible into faunal and lithologic zones or phases. In ascending order they are: (1) massive earthy brownish-gray limestone with mixed molluscan, crinoid, and brachiopod faunas, (2) thinner bedded limestone with fusulines, brachiopods, and crinoid remains, or locally Chaetetes colonies, and (3) slabby impure limestone. In northern Oklahoma and southern Kansas the Myrick Station limestone is overlain by gray marine shale or locally by black shale, or again locally there is no shale between it and the overlying Laberdie limestone. Obviously the sea did not withdraw from this area at the end of the cyclothem (pl. 2). In western Missouri and neighboring parts of Kansas the lower part of the Mine Creek shale may be in part nonmarine and certainly records near-shore conditions. Locally in western Missouri the lower part of the Pawnee limestone is well developed (pl. 2, secs. 181, 182, and 185). Elsewhere, for example in several exposures in Bates County, the Myrick Station limestone and the black shale and the thin limestone of the Anna shale seem to be completely absent. The lowermost Pawnee beds in those exposures are those in the upper part of the Mine Creek shale, which consist of calcareous fossiliferous shale and limestone nodules and are widespread over western Missouri and eastern Kansas.

The Mine Creek cyclothem is aberrant and somewhat local. In eastern Kansas it consists of the lower part of black or gray marine shale, then thin limestone and brachiopod coquinas that are overlain by black or gray shale beds (pl. 2).

The Laberdie cyclothem begins with black shale or with fossiliferous gray shale which is classified as the upper part of the Mine Creek shale. Phases in the Laberdie limestone are not readily differentiated. Chaetetes colonies were established locally almost at the beginning of limestone deposition. They became more numerous and larger as limestone deposition proceeded. Fusulines, brachiopods, and crinoid remains are, it seems, not confined to definite zones.

The sea withdrew from a large area including much of eastern Kansas and western Missouri soon after the end of Laberdie deposition. The persistence of the Mulberry coal bed and its "underclay" offers the strongest evidence for this statement. It is significant that the Mulberry coal has been identified in the subsurface in eastern Nebraska. Locally, however, the absence of the sea was of short duration, for in some places in eastern Kansas and neighboring parts of Missouri a thin limestone bed was deposited a few inches above the Mulberry coal. Thus it seems that the Mulberry cyclothem should be grouped with other cyclothems in the Pawnee megacyclothem. The end of the megacyclothem is marked by erosion that preceded deposition of the channel sandstone of the Bandera Quarry sandstone.

The Altamont Megacyclothem

The Altamont megacyclothem is somewhat unique. Its chief characteristic is the great lateral persistency of carbonaceous shale containing phosphatic nodules that are unlike the small smooth nearly spherical nodules found in other dark shales in Marmaton rocks. These nodules are in the Lake Neosho shale. They are rough, irregular in form, and gray in color. They contain teeth and other remains of vertebrate animals. They may be coprolites.

The Altamont megacyclothem (pl. 3) begins with the Bandera Quarry sandstone, a part of which fills channels cut in clay shale of the lower part of the Bandera shale. Throughout a large area there is a maroon band in the upper part of the Bandera shales above the sandstone phase. Locally in Labette County, a thin coal bed that has characteristics of coal formed at the place in which the plant material grew occurs in the upper part of the Bandera shale. This coal is above the maroon zone and a few inches below the Altamont limestone. There is a coal bed in the same stratigraphic position in northern Missouri and southern Iowa (Cline, 1941, pp. 26, 27, fig. 2). It is believed that in Kansas a large amount of the clay and sandy shale in the upper part of the Bandera formation is nonmarine. The Altamont limestone comprises the dominantly calcareous part of the megacyclothem, which closes with coarse clastic deposits or with shale beds next below sandstone in the Nowata shale. Cyclothems that are locally detectable and compose the larger cycle, named in upward order, are: (1) the Lower Tina cyclothem, (2) the Middle Tina cyclothem, (3) the Upper Tina cyclothem, and (4) the Worland cyclothem. In most parts of the Altamont limestone outcrop area, the Tina limestone comprises the limestone phase of a single cyclothem. Cline (1941, p. 60) recognized the "Tina cyclothem" as far north as Adair County, Missouri. However, in accordance with the use of the term cyclothem adopted in this paper, locally three cyclothems can be detected in the lower part of the Altamont rocks.

The Lower Tina cyclothem begins with coal and other nonmarine rocks in the upper part of the Bandera shale. Locally the upper part of the Bandera shale is undoubtedly marine, showing that the sea was present in certain places before limestone deposition started (pl. 3, sec. 171). Limestone was deposited only locally during the Lower Tina cycle. This limestone is darkish-gray, mottled, and contains chonetid brachiopods including plentiful Mesolobus. It is easily distinguished from other parts of the Tina limestone. The closing stages of the cycle are represented by very thin beds of marine shale. The Lower Tina cyclothem has been seen in Bates County, Missouri, and in Neosho County, Kansas.

The Middle Tina cycle, like the Lower, is local in occurrence. The two can be seen in the same places. The Middle cyclothem, however, contains the thickest bed of limestone in the Tina deposits. The opening phase of this cycle is not divided from the closing phase of the underlying cycle, but marine shale is followed by fusuline-bearing limestone. This limestone is overlain by limestone containing a mixed molluscan and bryozoan fauna. This is followed by less pure limestone bearing, brachiopods and crinoids. The cycle ends and the next higher one begins with thin beds of marine shale.

The limestone phase of the Upper Tina cyclothem is extremely widespread. This is believed to be the part of the Tina limestone that persists, with only a few local areas of nondeposition, from northeastern Oklahoma to northern Missouri. Throughout most of the outcrop area it shows evidence of having been deposited in very shallow water. It is sandy and locally grades into siltstone and sandstone. In many Kansas outcrops it is brecciated and cross-bedded as though loose limy pellets and animal remains were shifted by waves or currents before being cemented into a compact bed. This facies commonly bears a gastropod fauna mixed with algal remains, or in some places it is a mass of ostracodes, brachiopods, and algae. Attention is called to the analogy of this persistent limestone to "super" limestone of the Shawnee (Virgilian) cyclic deposits (Moore, 1936, p. 27) and to the "battlefield-beds" of Mesozoic cycles (Arkell, 1933, p. 57). Frebold (1927, p. 240) believed that each bed of this kind represents a shallowing of the sea and a prolonged pause.

Chaetetes were important rock builders throughout most of the time of Tina deposition. In southern Kansas, immediately south of the area in which Tina cycles can best be differentiated, most of the Tina section is composed of Chaetetes masses. The colonies seem to have gained a footing soon after the beginning of deposition of the limestone phase of the Lower Tina cyclothem, and the corals continued to flourish in areas that were protected from incoming clays during the waning and waxing of Tina cycles. Thus aided by accumulations of calcareous algae they continued to build up limestone masses until covered by muds that now form the Lake Neosho shale.

Black shale containing coprolites (?), underlain and overlain by gray shale, marks the transition from the Upper Tina cyclothem into the Worland cycle. The zone of phosphatic nodules extends far to the north and, as can be detected from Cline's sections (1941 pp. 33, 40, and 52), it actually belongs to the Worland cycle rather than to the Tina cycle. In northern Missouri Cline found a widespread coal smut between the Tina limestone and the zone of phosphatic nodules.

The Worland limestone in Kansas is not readily divisible into phases. Fusulines and brachiopods are dispersed throughout its thickness. Chaetetes colonies to my knowledge do not occur in the Worland limestone in Kansas, but they are plentiful in this rock in Missouri (Cline, 1941, p. 43), where Cline found cyclic phases to be more easily differentiated.

The Altamont megacyclothem closes with elastic deposits in the lower part of the Nowata shale. As already explained, it is probable that in eastern Kansas there is a hiatus above the Altamont limestone and that dark shale, for convenience classed in the Nowata formation, actually represents early phases of the Lenapah cycle. Coal is not known to occur in the lower part of the Nowata shale in Kansas but Cline found coal underlain by underclay in this part of the stratigraphic section rather generally in Missouri (Cline, 1941, pp. 26-27, fig. 2).

The Lenapah Megacyclothem

Although the Lenapah limestone is inconspicuous throughout its line of outcrop north of Labette County, Kansas, and it was only recently known to extend across the state into Missouri, its cyclic elements can be identified along a line extending many miles. The Lenapah formation, like the older Marmaton limestone formations, contains the more calcareous part of a megacyclothem. In the southern part of the Kansas outcrop area it is separated here and there from the Altamont limestone by a thick elastic deposit, much of which is sandstone (pl. 4, sec. 178); part of the sandstone probably occurs as channel fillings. Abrupt changes in thickness of the clastic deposits between the two limestones suggest that there was erosion of Nowata shale beds before the advent of the Lenapah cycle, that there was considerable differential subsidence prior to Lenapah deposition, or both (pl. 4). The megacycle began with deposition of clastic material, much of which is sandstone. It passes into a more calcareous phase, then into one of clastic deposition, and the cycle closes with erosion that marked the end of Desmoinesian time. Like other Marmaton limestones, the Lenapah is overlain closely by "underclay" and 'Coal (pl. 4, secs. 135 and 156).

The Lenapah formation, when studied in detail, shows evidence of cyclic deposition within the formation and hence, with underlying and overlying beds, it is regarded as composing a megacyclothem. The included cyclothems, named in ascending order, are: (1) the Norfleet cyclothem, (2) the Perry Farm cyclothem, and (3) the Idenbro cyclothem. All of the cyclothems are more or less aberrant and the phases are of rather local occurrence. The cyclothems are not readily detectable in northern Oklahoma. The Norfleet cyclothem begins with sandstone and shale, overlain by black shale. Locally gray shale overlies black shale and underlies the Norfleet limestone. The Norfleet limestone, which has several facies varying from massive brachiopod-bearing dark-brown limestone through slabby limestone containing land-plant fossils into alternating beds of impure limestone and shale, records a variety of conditions, differing probably in part because of configuration of the shore line which must have been near the locations of some of the present outcrops. Gray and black shale overlying the Norfleet limestone records the closing stages of the cycle.

The Perry Farm cyclothem is similar to the Mine Creek cyclothem in the Pawnee megacycle. Its middle phase is poorly developed, being represented by thin limestone beds, by limestone nodules, and by shale with many marine fossils. Its opening and closing stages are locally represented by black and gray shale, but commonly one or more phases are absent from any one outcrop.

The Idenbro cyclothem records the most prolonged period of deepened water in the megacycle, and the Idenbro limestone is the member of the Lenapah formation that extends far to the north.east. The cycle began with the deposition of black shale which is overlain by calcareous fossiliferous shale. This in turn is overlain by the Idenbro limestone, whose base is generally transitional from the shale below. Throughout large areas in southeastern Kansas and in neighboring parts of Oklahoma, the Idenbro limestone shows evidence of having been formed in clear water, although locally the basal part is argillaceous and the whole limestone is more siliceous than are the other Marmaton limestones. The argillaceous limestone phase is overlain by thin wavy-bedded purer limestone. Cup corals and brachiopods are dispersed throughout the thickness of the rock, but algal remains are confined largely to the upper and lower parts.

In northern Oklahoma limestone deposition continued from the Norfleet cycle to about the close of the Perry Farm cycle (pl. 4, secs. 199 and 200). In eastern Missouri all Lenapah cyclothems are detectable but the limestone phases are very thin (pl. 4, secs. 180 and 181a).

The closing phases of the Idenbro cyclothem are not well recorded. A succession of "underclay," coal, and black shale occurring next above the Idenbro limestone (pl. 4, sec. 156) probably belongs in the Idenbro cyclothem. Cyclic deposits higher in the Memorial shale have not been detected. It is probable that in eastern Kansas the Idenbro cycle was the last in Desmoinesian time.